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Astronomical year numbering
Astronomical year numbering is based on / year numbering, but follows normal numbering more strictly. Thus, it has a , the years before that are designated with s and the years after that are designated with positive numbers. Astronomers use the for years before 1582, including this year 0, and the for years after 1582 as exemplified by (1740),Jacques Cassini, Tables Astronomiques (1740), Explication et Usage pp. 5 (PA5), 7 (PA7), Tables pp. 10 (RA1-PA10), 22 (RA1-PA22), 63 (RA1-PA63), 77 (RA1-PA77), 91 (RA1-PA91), 105 (RA1-PA105), 119 (RA1-PA119). (1898)Simon Newcomb, "Tables of the motion of the Earth on its axis and around the Sun" in Astronomical papers prepared for the use of the American ephemeris and Nautical Almanac, Volume VI: Tables of the four inner planets, (United States Naval Observatory, 1898), pp. 27 (PT36), 34–35 (PT43–PT44). and (2007).Fred Espenak, Phases of the Moon: −99 to 0 (100 to 1 BCE) NASA Eclipse web site The prefix AD and the suffixes CE, BC or BCE (Common Era, Before Christ or Before Common Era) are dropped. The year 1 BC/BCE is numbered 0, the year 2 BC is numbered −1, and in general the year n'' BC/BCE is numbered "−(''n − 1)" (a negative number equal to 1 − n''). The numbers of AD/CE years are not changed and are written with either no sign or a positive sign; thus in general ''n AD/CE is simply n'' or +''n. For normal calculation a is often needed, here most notably when calculating the number of years in a period that spans the ; the end years need only be subtracted from each other. The system is so named due to its use in . Few other disciplines outside deal with the time before year 1, exceptions being , and , the latter two of which use ' '. Although the absolute numerical values of astronomical and historical years only differ by one before year 1, this difference is critical when calculating astronomical events like eclipses or planetary conjunctions to determine when historical events which mention them occurred. Year zero usage In his (1627), used a prototype of year zero which he labeled Christi (Christ) between years labeled Ante Christum (Before Christ) and Post Christum (After Christ) on the mean motion tables for the Sun, Moon, Saturn, Jupiter, Mars, Venus and Mercury.Johannes Kepler, Tabulae Rudolphinae (1627) Pars secunda, 42 (Zu Seite 191), 48 (197), 54 (203), 60 (209), 66 (215), 72 (221), 78 (227). (Latin) Then in 1702 the French astronomer used a year he labeled at the end of years labeled ante Christum (BC), and immediately before years labeled post Christum (AD) on the mean motion pages in his Tabulæ Astronomicæ, thus adding the designation 0'' to Kepler's ''Christi.Tabulae Astronomicae - Philippo de la Hire (1702), Tabulæ 15, 21, 39, 47, 55, 63, 71; Usus tabularum 4. (Latin) Finally, in 1740 the French astronomer , who is traditionally credited with the invention of year zero,Robert Kaplan, [http://books.google.com/books?id=Bn0EBVsfi1YC&pg=PA103 The nothing that is] (Oxford: Oxford University Press, 2000) 103.Dick Teresi, "Zero", The Atlantic, July 1997 (see under Calendars and the Cosmos).L. E. Doggett, "Calendars", Explanatory Supplement to the Astronomical Almanac, ed. P. Kenneth Seidelmann, (Sausalito, California: University Science Books, 1992/2005) 579. completed the transition in his Tables astronomiques, simply labeling this year 0'', which he placed at the end of Julian years labeled ''avant Jesus-Christ (before Jesus Christ or BC), and immediately before Julian years labeled après Jesus-Christ (after Jesus Christ or AD). Cassini gave the following reasons for using a year 0:Jacques Cassini, Tables Astronomiques, Explication et Usage 5, translated by Wikipedia from the French: "L'année 0 est celle dans laquelle on suppose qu'est né J. C. que plusieurs Chronologistes marquent 1 avant la naissance de J. C. & que nous avons marquée 0, afin que la somme des années avant & après J. C. donne l'intervalle qui est entre ces années, & que les nombres disibles par 4 marquent les années bissextiles tant avant qu'après J. C." Fred Espanak of lists 50 phases of the moon within year 0, showing that it is a full year, not an instant in time. Jean Meeus gives the following explanation:Jean Meeus, Astronomical Algorithms (Richmond, Virginia: Willmann-Bell, 1991) 60. Signed years without year 0 Although he used the usual French terms "avant J.-C." (before Jesus Christ) and "après J.-C." (after Jesus Christ) to label years elsewhere in his book, the Byzantine historian Venance Grumel used negative years (identified by a minus sign, −) to label BC years and unsigned positive years to label AD years in a table, possibly to save space, without a year 0 between them.V. Grumel, La chronologie (Paris: Presses Universitaires de France, 1958) 30. The , sometimes used in connection with representing data for storage in computers, contains built-in primitive datatypes, date and dateTime, which do not allow a year zero, and designate years BC as negative numbers. Years contain at least four digits. Thus -0001 in that language is equivalent to 1 BC. However, the defining indicates a change to a system similar to and astronomical year numbering is likely in the future.Biron, P.V. & Malhotra, A. (Eds.). (28 October 2004). [http://www.w3.org/TR/xmlschema-2/#dateTime XML Schema Part 2: Datatypes (2nd ed.).] World Wide Web Consortium. See also * * References Category:Calendar eras Category:Chronology